Luminiferous Aether

The luminiferous aether theory held that light, understood as a wave, needed a physical medium to travel through, filling all of space including a vacuum, and that this medium had to be almost rigid to support light's high frequency while offering no detectable resistance to planets moving through it. Building on Christiaan Huygens's seventeenth century wave theory of light, nineteenth century physicists developed the aether idea to explain how a wave could cross empty space at all. The 1887 Michelson-Morley experiment looked for Earth's motion through the aether by comparing light's speed in different directions and found no difference whatsoever, a null result the aether theory could not explain. Einstein's 1905 special relativity showed the same physics could be derived without any aether, and the theory was abandoned.